1. Field of the Invention
The present invention relates to an optical element for controlling the amount of light transmitted as a ray bundle through an optical system, i.e., an optical filter, and to a photo-taking device using the optical element. More particularly, the present invention aims to realize an optical element which can be designed so as to be smaller in size, capable of efficiently controlling the amount of transmitted light by simple construction, and which is suitable for forming a variable neutral density filter (variable ND filter), an apodization filter, a filter for correcting a reduction of marginal light, etc., an optical system formed by a lens unit incorporating an aperture or shutter constituted by the optical element, and a photo-taking device using such an optical system.
2. Related Background Art
Conventionally, photo-taking optical systems for use in photo-taking devices such as still and video cameras need to have a focusing function, a light quantity control function, a function for a natural softfocus effect, a function for uniformly distributing a quantity of light at the image plane, etc.
For the light quantity control function in these functions, a mechanical aperture formed of a plurality of movable blades is generally used.
Such a mechanical diaphragm, however, necessitates a mechanical driving system, which increases the overall size of a device incorporating the mechanical aperture and the drive. Also, such a mechanical diaphragm has the problem of diffraction of rays under a small-aperture condition causing a reduction in the resolution of a formed image.
To avoid such a problem, a variable transmittance element using a liquid crystal material or an electrochromic material, i.e., a variable ND (Neutral Density) filter, has been proposed.
For example, Japanese Patent Application Laid-open No. 3-87816 discloses an electrochromic optical modulator designed so as to prevent a non-uniformity of color of transmitted light.
Japanese Patent Application Laid-open No. 7-5497 discloses a technique for realizing a variable ND filter by enabling silver in a solution to precipitate and dissolve freely.
Japanese Patent Application Laid-open No. 7-128635 discloses a technique for adjusting the quantity of light entering a photoelectric converter by using a liquid crystal filter that has variable density.
Japanese Patent Application Laid-open No. 9-236740 discloses, as a technique for realizing a natural softfocus effect a technique relative to an apodization filter formed by combining a planoconcave lens having a large light absorption coefficient with a planoconvex lens having a small light absorption coefficient.
As a technique for correction of marginal light quantity reduction on the imaging plane Japanese Patent Application Laid-open No. 9-15681 discloses a light quantity adjustment technique using a liquid crystal variable ND filter having a higher density at its center and capable of density control.
Further, WO99/18456 discloses a variable-focus lens based on electrocapillarity (electrowetting phenomenon). If this art is used, electrical energy can be directly used for changing the shape of a lens, thereby enabling focus control without any mechanical lens movement.
One aspect of the application the present invention relates to an object for providing an optical device comprising as an optical element a container and first and second liquids sealingly or hermetically contained in the container, the first and second liquids being substantially equal in refractive index, the first and second liquids existing without mixing with each other, the first and second liquids differing from each other in transmittance, the first and second liquids being sealingly contained in the container with the boundary between the first and second liquids having a predetermined shape, and an electrode formed in such a place as to avoid interference with passage of a bundle of rays incident into the optical element, wherein a voltage is applied to the electrode to change the transmittance with respect to the bundle of rays.
Another aspect of the application of the present invention relates to an object for providing an optical device comprising an optical element having a container having a side surface inclined at a predetermined angle from an optical axis, and first and second liquids contained sealingly or hermetically in the container, the first and second liquids differing substantially from each other in transmittance, the first and second liquids existing without mixing with each other, the first and second liquids being contained in the container with the boundary between the first and second liquids having a rounded shape, and an electrode formed in such a place as to avoid interference with passage of a bundle of rays incident into the optical element, wherein a voltage is applied to the electrode to change the refractive index of the optical element.
Another aspect of the application of the present invention relates to an object for providing an optical device comprising a lens element and at least one of a diaphragm and a shutter incorporated in the lens element.
These and other objects, features and advantages of the present invention will become apparent from the detailed description of embodiments of the invention taken in conjunction with the accompanying drawings.